Ultrasound imaging, in which ultrasound images are generated by detecting ultrasonic waves which are reflected within the body of a subject by the ultrasonic waves being emitted within the body of the subject, to enable display of morphological tomographic images, is known as a conventional method for obtaining tomographic images of the interior of the body of a subject. Meanwhile, there have been recent advancements in the development of apparatuses which are capable of displaying not only morphological tomographic images but also functional tomographic images in examinations of subjects. One such apparatus is that which utilizes the photoacoustic analysis method. The photoacoustic analysis method emits light having a predetermined wavelength (visible light, near infrared light, or intermediate infrared light, for example) onto a subject, detects photoacoustic waves, which are elastic waves generated as a result of a specific substance within the subject absorbing the energy of the light, and quantitatively measures the concentration of the specific substance. The specific substance within the subject is glucose, hemoglobin, etc., which is included in blood. The technique that detects photoacoustic waves and generates photoacoustic images based on detected signals is referred to as PAI (Photo Acoustic Imaging) or PAT (Photo Acoustic Tomography).
Photoacoustic imaging images objects that have higher coefficients of light absorption than that of media that surround the objects. For example, the coefficient of light absorption of blood vessels within bodies is greater than that of the media that surrounds them, and imaging of blood vessels is being widely researched.
For example, it is known that photoacoustic waves which are generated from tissue systems having high coefficients of light absorption such as blood vessels are detected as N shaped acoustic signals as illustrated in FIG. 6A (Japanese Unexamined Patent Publication No. 2010-136887). Generally, the amount of time t between emission of light until detection of these acoustic signals is a value that reflects the position of the blood vessels with respect to a detector, and the width w of the acoustic signals is a value that reflects the size of the blood vessels. Coefficients of light absorption are calculated based on the photoacoustic waves described above, and photoacoustic images are obtained as a distribution of coefficients of light absorption.